1. Field of the Invention
The invention relates to data recording/reproducing apparatus and method corresponding to a plurality of data formats and a data recording medium.
2. Description of the Prior Art
As an external memory apparatus of a computer, attention is paid to an optical disc drive from a viewpoint of advantages of large capacity and high-speed access. The use of a CD-ROM (or CD-I (CD Interactive)) drive and an MO (magneto-optical disc serving as one of erasable discs) drive has already been rapidly spread. In addition to those discs, an MD (mini disc; erasable disc) having a disc diameter of 2.5 inches has also been proposed. Further, a DVD (digital video disc) is being developed as a video memory medium.
The DVD is a read only disc having the same diameter as that of the CD or a recordable/reproducible optical disc such as MO disc or phase-change type disc. The DVD is a disc in which video information compressed by MPEG or the like can be reproduced or can be recorded and reproduced. In the DVD, by the improvement of processes such as digital modulation and error correction encoding in association with the progress of the realization of a short wavelength of a laser beam and an increase in numerical aperture (NA) of an objective lens, a recording density is further raised. Even in the case of a single-layer disc, a data memory capacity is very large to be about 3.7 Gbytes. In a manner similar to the CD and MD which have first been developed as digital audio discs and, after that, also used as external memory media of computers, it is expected that the DVD having a larger capacity is used as an external memory medium of the computer.
Hitherto, since different formats have been specified for every medium such as magnetic tape, magnetic disc, flexible disc, above-mentioned optical discs, and the like, respectively, a consideration about compatibility is not made. Therefore, in the case of obtaining compatibility between a new medium and the existing medium, such compatibility can correspond in only a logical region, so that it is not efficient. For example, in case of an external memory medium of a computer, a sector size of (128 bytes.times.2.sup.i)(512 bytes, 2 kbytes, or the like) is a main stream. In the CD-ROM, 2352 bytes (in case of excluding a synch signal, 2340 bytes; in case of excluding the synch signal and a header, 2336 bytes) is set to one block. Thus, there is a problem such that it is difficult for both of them to physically correspond to each other. Further, as a sector size according to the CD format including the CD-ROM, when considering a sub-code as well, there are other various sizes.
The above-mentioned DVD can be realized even by a recordable MO disc or a phase-change type disc, so that there is an advantage such that when compared with a capacity of any one of the other existing optical discs, a capacity of the DVD is remarkably large. In the case of newly using such a DVD as an external memory medium, it is indispensable to consider the compatibility with the existing optical disc media, especially, the CD-ROM which has been widespread and has almost the same disc size and uses the same reading method in order to simplify the mutual transmission and reception of data between the CD-ROM and the DVD, to enable the drive to be shared, and further, to effectively use the resources of the CD-ROM.
In JP-A-7-73593, the inventors of the present invention have proposed the method of setting a memory capacity per one recording block unit of the MO disc to 2352 bytes in order to simplify the data transmission and reception between the CD-ROM and the MO disc. According to the method, the memory capacity per one recording block of the MO disc is matched with that of the CD-ROM. There is a problem such that although such a method can be applied to a case where a data structure of the disc is newly decided, it cannot be applied to a case where the data structure of the disc has been standardized to a certain degree.
As mentioned above, in the data recording/reproducing apparatus in which a plurality of sector sizes are permitted, ordinarily, a different format is specified for every data having a different sector size and signal processes for recording and reproduction are made independent every format. According to such a method, there is a problem that a scale of hardware for recording and reproduction increases. As another approach, there is a method whereby data having different sector sizes is fundamentally recorded and reproduced in the same format, an identification (ID) signal is inserted to a directory area or a header area as additional information, and the sector size is recognized by the ID signal.
The method of inserting the ID information of a sector size into the additional information has an advantage such that a hardware can be partially shared. However, there is a problem with respect to a point of an accessing performance. Generally, in case of recording and reproducing digital data, a digital modulation such as an EFM or the like is generally performed to data in order to improve an error rate and to enable a clock to be easily extracted. The additional information as mentioned above has also been modulated. Therefore, the ID information cannot be obtained upon reproduction unless a process for demodulation is finished. A sector size of data which was reproduced so far cannot be known, so that the accessing performance deteriorates.